C64 BASIC is kind of a mess, there's zero support for graphics and sound. Your code rapidly becomes a giant pile of POKEs and PEEKs, and all your operations become absurdly slow because all the math routines are floating point only, so there's a ton of integer/fp conversion overhead on something as simple as "peek a memory location, AND/OR it with a few values taken from variables stored as floating point, poke it back".

Assembly becomes really attractive really quickly.

BBC BASIC was far better than C64 BASIC.

It had a nice set of built-in graphics functions and an inline assembler, amongst other things.

I can still remember that VDU 23 was the command to redefine a character, so much easier than doing the same sort of thing on the C64 (copy the character set from ROM to RAM, get the VIC to use the RAM copy with POKE statements, modify the desired character)